Zinc ion has been used in oral products for some time now. In dentifrices, it has been employed as a tartar control agent. In mouthwashes as well as elsewhere, it is used as a bacteriocide (U.S. Pat. No. 5,455,023, incorporated herein by reference) and to combat malodor. In other products it has been used as a bacteriocide or as a fungicide. Zinc undecylenate, for example is a water insoluble antifungal. Zinc tannate, zinc carbonate, and zinc peroxide are antiseptic/astringents which are practically insoluble in water. Zinc phenolsulfonate is an astringent. Zinc sulfate has been used as an ophthalmic astringent and as a zinc supplement. Zinc salicylate, zinc permanganate, and zinc stearate are antiseptic/astringents. Zinc pyrithione is a fungicide, bacteriocide, and antiseborrheic; it is the active agent in Head & Shoulders brand shampoo. Zinc propionate is a topical antifungal. Zinc oxide is an astringent/protectorant. Zinc nitrate is used in dying textiles. Zinc metaarsenate is a wood preservative and insecticide. Zinc iodide is an antiseptic/astringent. Zinc iodate is an antiseptic. Zinc chloride is an astringent. All of these can be found in The Merck Index, 12th Edition, Merck & Co. (Whitehouse Station, N.J. 1996). Zinc borate, zinc caprylate, and zinc ricinolate are fungicides. Bicarbonate compounds have been used in oral care products for a variety of purposes including, but not limited to, buffering capacity, as alkalinizing agents, as abrasives (as solid particles), for deodorizing activity, and providing for a clean "mouthfeel" and a refreshing aftertaste in the oral cavity. Exemplary patents dealing with mouthwashes or rinses having bicarbonate included include, but are not limited to U.S. Pat. No. 4,132,770; U.S. Pat. No. 4,312,889; U.S. Pat. No. 4,666,708; U.S. Pat. No. 5,185,153; U.S. Pat. No. 5,302,373; U.S. Pat. No. 5,330,749, U.S. Pat. No. 5,455,023; U.S. Pat. No. 5,541,165; and U.S. Pat. No. 5,587,147; all of which are incorporated herein by reference. Carbonates or mixtures of carbonates and bicarbonates have been used similarly where the desired pH is not high enough when using bicarbonate compounds alone. Carbonates, especially alkali metal carbonates, have also been used extensively in the detergent (especially laundry and dishwashing) and household and industrial cleaner fields primarily as alkalinity providers or builders.
It has therefore been deemed advantageous to try to combine, in a single phase of a formulation, both zinc ion containing compounds and bicarbonate and/or carbonate ion containing compounds, each of which is in solution. Unfortunately this has not been possible previously. Zinc ion typically reacts with bicarbonate ion to result in liberation of carbon dioxide and the formation of various insoluble basic salts of zinc and carbonate. Attempts to get around this technical difficulty have included keeping the two components separated in different compartments or containers until ready for use; encapsulating one or both of the ingredients; or presenting one or both of the components in less soluble form so that the two species are in limited contact until diluted by the user in the course of using the product, among others.
Examples of encapsulating one or both components include U.S. Pat. No. 5,302,373; U.S. Pat. No. 5,330,749; and U.S. Pat. No. 5,455,023. Examples of dual compartment dispensing include U.S. Pat. No. 5,456,902; U.S. Pat. No. 5,554,358; U.S. Pat. No. 5,616,313; and U.S. Pat. No. 5,632,972. Examples of complexation include U.S. Pat. No. 5,587,147. All of the foregoing U.S. patents are incorporated herein by reference. Typical of the presentation of one or more of the components in an insoluble or slightly soluble form until use is in the toothpaste, tooth gel and tooth powder areas where their remaining in solution during storage may not be as critical a requirement to meet. (Notwithstanding this lack of criticality for keeping the zinc ion and the bicarbonate and/or carbonate ion in solution, it is still highly desirable to maintain both components in solution above the concentrations that would be achieved without the solubilizing anion of the invention.)
However, many liquid products (such as mouthwashes and many other applications mentioned above) cannot present with precipitates during storage and still be considered suitable delivery vehicles for the components they contain. Haircare products are typically in contact with the scalp for such a short period of time that dissolution of particulate zinc compounds, especially zinc carbonates (inclusive of bicarbonates and sesquicarbonates), to obtain the benefit of zinc ion is truly not a suitable result. Furthermore, many of the applications above require clarity for improved consumer acceptance or aesthetics. Additionally, dual dispensing systems are inconvenient for the user and generally not desirable. As such, there has been a long felt need for a single phase stable solution having both zinc ion and bicarbonate and/or carbonate ion, each in solution.